Remember that iMessage does allow you to still send a message as a text. When you tap send quickly tap and hold the message and choose "Send as text message". You can also do this if you try and resend a failed iMessage.

Down here for me too. I sent a message to my wife on her @me.com account and it says it can't deliver it. But sending it to her to her iPhone account sends a text message via the AT&T Text messaging service...which is "green" on the iPhone iMessage app...so it just cost me .25 cents to send it when normally it would be free.

Sending it to her on her @me.com account says "This person cannot be reached by iMessage at this time".